Add a description field for email interests

Currently the system only allows for a list of email interests with no ability to indicate the meaning. This means that we have no way of offering to the donor a value proposition for receiving that type of email. Without that, many donors opt out of all emails because they have not been provided a reason why they would want the email and how frequently they will receive them. Without seeing more information the thought is "its just another email".

This is important, because when a donor clicks on a email to opt-out, they see the whole menu of email interests and then, because they are taking action based on the current content, they just automatically opt out of all emails. If we could provide a value proposition and expectation, they will be less likely to opt out of all emails if they resonate with the description of at least one of the topic areas.